package com.parkwalk.xxx.ui.security;

import java.util.zip.Checksum;

public class CRC16 implements Checksum {
    private static final int[] CRC_TABLE = {0, 49345, 49537, 320, 49921, 960,
            640, 49729, 50689, 1728, 1920, 51009, 1280, 50625, 50305, 1088,
            52225, 3264, 3456, 52545, 3840, 53185, 52865, 3648, 2560, 51905,
            52097, 2880, 51457, 2496, 2176, 51265, 55297, 6336, 6528, 55617,
            6912, 56257, 55937, 6720, 7680, 57025, 57217, 8000, 56577, 7616,
            7296, 56385, 5120, 54465, 54657, 5440, 55041, 6080, 5760, 54849,
            53761, 4800, 4992, 54081, 4352, 53697, 53377, 4160, 61441, 12480,
            12672, 61761, 13056, 62401, 62081, 12864, 13824, 63169, 63361,
            14144, 62721, 13760, 13440, 62529, 15360, 64705, 64897, 15680,
            65281, 16320, 16000, 65089, 64001, 15040, 15232, 64321, 14592,
            63937, 63617, 14400, 10240, 59585, 59777, 10560, 60161, 11200,
            10880, 59969, 60929, 11968, 12160, 61249, 11520, 60865, 60545,
            11328, 58369, 9408, 9600, 58689, 9984, 59329, 59009, 9792, 8704,
            58049, 58241, 9024, 57601, 8640, 8320, 57409, 40961, 24768, 24960,
            41281, 25344, 41921, 41601, 25152, 26112, 42689, 42881, 26432,
            42241, 26048, 25728, 42049, 27648, 44225, 44417, 27968, 44801,
            28608, 28288, 44609, 43521, 27328, 27520, 43841, 26880, 43457,
            43137, 26688, 30720, 47297, 47489, 31040, 47873, 31680, 31360,
            47681, 48641, 32448, 32640, 48961, 32000, 48577, 48257, 31808,
            46081, 29888, 30080, 46401, 30464, 47041, 46721, 30272, 29184,
            45761, 45953, 29504, 45313, 29120, 28800, 45121, 20480, 37057,
            37249, 20800, 37633, 21440, 21120, 37441, 38401, 22208, 22400,
            38721, 21760, 38337, 38017, 21568, 39937, 23744, 23936, 40257,
            24320, 40897, 40577, 24128, 23040, 39617, 39809, 23360, 39169,
            22976, 22656, 38977, 34817, 18624, 18816, 35137, 19200, 35777,
            35457, 19008, 19968, 36545, 36737, 20288, 36097, 19904, 19584,
            35905, 17408, 33985, 34177, 17728, 34561, 18368, 18048, 34369,
            33281, 17088, 17280, 33601, 16640, 33217, 32897, 16448};
    private int crc;

    public long getValue() {
        return this.crc & 0xFFFFFFFF;
    }

    public void reset() {
        this.crc = 0;
    }

    public void update(byte[] b) {
        this.crc = updateBytes(this.crc, b, 0, b.length);
    }

    public void update(byte[] b, int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        }
        if ((off < 0) || (len < 0) || (off > b.length - len)) {
            throw new ArrayIndexOutOfBoundsException();
        }

        this.crc = updateBytes(this.crc, b, off, len);
    }

    public void update(int b) {
        this.crc = update(this.crc, b);
    }

    private int update(int crc, int b) {
        crc = crc >>> 8 ^ CRC_TABLE[((crc ^ b) & 0xFF)];
        return crc;
    }

    private int updateBytes(int crc, byte[] b, int off, int len) {
        for (int i = off; i < off + len; i++) {
            crc = update(crc, b[i]);
        }

        return crc;
    }
}